1. Field of the Invention
The present invention relates to displacement detecting devices used in positioning and in detecting a displacement in a linear direction, in a machine tool, an industrial machine, a robot, and the like.
2. Description of the Related Art
Conventionally, a displacement detecting device including a scale and a detection head has been used in order to detect a linear movement amount and a linear position in positioning, in controlling, for position display and the like of a machine tool, an industrial machine, a robot, and the like. Furthermore, in recent years, there has been also proposed a displacement detecting device that detects not only a displacement (movement) of a detection head but also an absolute position of the detection head with respect to a scale by detecting an origin mark through the use of a vernier-type scale.
Examples of such a conventional displacement detecting device include the displacement detecting device described in, for example, Patent Literature 1. The displacement detecting device described in Patent Literature 1 includes a scale having formed therein a first region, in which positional information is recorded at predetermined intervals, and a second region, in which positional information is recorded at intervals different from the intervals of the first region. Furthermore, the displacement detecting device described in Patent Literature 1 (Japanese Laid-Open Patent Publication No. 2004-170153) includes a first reader configured to read positional information in the first region and a second reader configured to read positional information in the second region.
In addition, in the displacement detecting device described in Patent Literature 1, an origin signal is generated when a difference between a first phase detected by reading positional information in the first region and a second phase detected by reading positional information in the second region becomes an arbitrarily set value. With the origin signal used as a reference, the absolute position of the detection head with respect to the scale is detected. Namely, in the displacement detecting device described in Patent Literature 1, the origin mark is arbitrarily formed using a phase difference between the first region and the second region.